Colossal flames hurtled into the air over a Queens bus depot rocked by explosions yesterday as workers offloaded a storage tank of compressed natural gas, officials said.

“We heard a boom, then we saw flames, and the earth shook,” said bus driver Mark Lawrence, who was set to begin his route at the MTA depot in East Elmhurst but fled when he heard a blast at 10:43 a.m. followed by another.

One person suffered minor injuries, and fire marshals were investigating the cause of the two-alarm blaze but believe “it does not appear to be construction-related, and it’s not suspicious,” said Fire Department spokesman Seth Andrews.

Two KeySpan workers were at the former Triboro Coach site to “decommission” the facility – that is, empty the tanks, because the MTA will no longer use the facility to fuel its buses with compressed natural gas.

“There had to be some kind of spark that created the ignition that lit the gas. We’re trying to determine what that was,” said KeySpan spokesman Jody Fisher.

The blast destroyed a bus as well as damaging 12 other buses and a depot tire shop.

“We thought it was a plane crash,” said Joe Sciortino, a bus driver who heard the blast.

MTA spokesman Tim O’Brien said, “We still have CNG buses in use, but as we buy new buses, we’re moving toward hybrid electric.”